It has up to now been customary to take out and measure a printed specimen. Thus, a continuous registration of the printed specimens is not possible. Further, the results cannot easily be assigned to the production process because the specimens are not automatically marked.
It has been proposed to provide rotational sheet printing machines with a sheet inspection system, arranged in an extended line of the sheet deposit where each sheet produced is photographed by several video cameras and compared with a so-called master sheet. Deviations of the quality produced from the quality of the master sheet will be indicated. In case of undue deviations the respective sheets can be marked or singled out. The measured values are not recorded.
The speed of the video cameras employed, to register the whole sheet, is relatively slow. For this very reason the known arrangement is not suitable for rotational roller printing machines. With a rotational sheet printing machine the relatively low speed is of minor importance, since the speed of production is only relatively low. Further, video cameras cannot register the spectral distribution, unless great efforts are made. Only the basic colors are therefore registered. To this end special filters are provided. The colors between the three basic colors have to be interpolated, thus resulting in relatively high inaccuracy.